Thermoplastic polyester materials have many commercial applications and are commonly used in fabrics, films and containers. Polyesters are popular due to their strength, flexural characteristics, clarity, thermal stability and food contact characteristics.
The compositions of the present invention were developed specifically for thermoforming processes which produce oriented, crystallized, clear (and transparent) articles. In such processes, the polyester is heat processed into a sheet and thereafter oriented, formed and heat set. These processing steps can be accomplished using conventional (or non-conventional) methods.
When such thermoforming processes use conventional polyester materials, cycle times are generally very long, making the process quite expensive and economically impractical. The long cycle times can be attributed to the slow crystallization rates of most conventional polyester resins. Conventional crystallization promoters (nucleants) can be added, but are generally detrimental to the properties, particularly the optical properties, of the final material.
A long-felt need therefore exists in the art for a polyester material having a high rate of crystallization (short cycle times), particularly when used according to the above described thermoforming processes. More particularly, after such processing, a long-felt need further exists for a final product having excellent clarity, transparency, heat stability, tensile strength, flexibility and the like.